Democratic Senate candidate Edward Markey released a new television ad on Thursday focusing on his role investigating the BP oil spill.

The ad shows photos of the Deepwater Horizon oil spill in the Gulf of Mexico, including the oil rig on fire and a bird covered in oil. BP was the company operating the oil rig when it exploded, killing 11 people and spilling millions of gallons of oil into the gulf.

“When BP tried to avoid responsibility, one man said no,” the ad states, flashing to a picture of Markey and news clips about Markey’s involvement in the issue. “Ed Markey uncovered the extent of the damage and when BP executives lied, Ed Markey held them accountable.”

The ad will air statewide.

As chairman of the Energy and Environment Subcommittee in the U.S. House, Markey was intimately involved in the investigation into the spill. Markey pressured BP to release accurate information regarding the rate at which oil was flowing into the water. Markey had argued that BP gave the public estimates of the flow that were too low.

Environmentalists have emerged as a key constituency for Markey. The League of Conservation Voters and the Sierra Club have both endorsed him, with the league announcing that it will spend $650,000 supporting Markey over his Democratic primary opponent, U.S. Rep. Stephen Lynch.

While both Lynch and Markey have strong voting records on environmental issues, Markey has written legislation on climate change and been a leader on issues such as the BP investigation. The climate change group 350.org and California clean energy activist Tom Steyer have supported Markey because of his opposition to the proposed Keystone XL oil pipeline, which Lynch supports.

Markey’s first ad focused on gun control policy. Lynch has generally focused on his biography and his blue collar roots in the two ads that he has released so far. None of the Republican Senate candidates have yet released any television ads.